Interactions of Supercritical CO2 with Coal

Carbon dioxide sequestration on coal with enhanced coalbed methane recovery (CO2-ECBM) is acknowledged as a promising way to mitigate CO2 emissions. For successfully understanding and implementing CO2-ECBM process, the potential interactions of CO2 with coal during CO2 sequestration in coal seams were investigated. Research methods consisting of low-temperature nitrogen adsorption–desorption and chromatographic analysis were used to address the transformation of coal pore morphology and the capability of supercritical CO2 extraction when coal contacts with high pressure CO2. According to the test results, interaction of coal with high pressure CO2 does not create a significant influence on pore shape and mesoporous volume distribution of any rank of coal. However, this causes the coal surface fractal dimension and specific surface area to be changed, which implies that the coal's pore morphology change due to CO2 sorption is irreversible. The results also indicate that the injection of high-pressure CO2 does not only change the pore morphology of coal but also has the ability to extract the hydrocarbons present in the coal matrix. The extracted hydrocarbons are of biological toxicity and can be mobilized with gas or water to other geologic structures and aquifers. Thus, the potential environmental safety and health issues (ES&H issues) related to CO2 sequestration in deep coal seams require thorough assessment.